LaCa2Fe2GaO8 adopts a 3-layer cation-ordered structure. Magnetisation data collected from this phase exhibit two high-temperature anomalies consistent with the onset of (antiferro)magnetic order. We propose to collect neutron powder diffraction data as a function of temperature to determine the complex cation-ordered and anion-vacancy ordered structure of LaCa2Fe2GaO8 and determine the magnetic ordering temperature and ordering scheme of this phase.Ca2(Cr0.75Ga0.25)GaO5 and LaCa2(Cr0.75Ga0.25)2GaO8 also adopt layered, cation-ordered structures, however they can only be prepared as single phases when they have gallium rich compositions. We propose to collect neutron powder diffraction data to perform a detailed structural characterisation so that we can better understand why phases with integer Cr:Ga rations cannot be prepared.